Technical Field
The present disclosure relates generally to instruments and methods for orthopedic spine surgery and, in particular, to a screw insertion instrument for selectively coupling to a pedicle screw and a method of operating the same.
Background of the Disclosure
Spinal fixation apparatus are widely employed in surgical processes for correcting spinal injuries and diseases. In order to facilitate stabilizing the spine and maintaining vertebral bodies in a desired alignment, implants such as longitudinally linked rods are secured to coupling elements, which in turn are secured to vertebral bodies by fasteners such as pedicle screws.
Many pedicle screws utilize a coupling element in the form of a tulip, which engages the pedicle screw head and is pivotable and rotatable in relation to the axis of the screw shank (i.e. polyaxial to the shank axis). While this ability more easily facilitates alignment of the tulip with the longitudinally linked rods, it may cause the screw to be difficult to handle. A means for ensuring the pedicle screw remains secured to an insertion instrument provides more positive control over the placement of the pedicle screw. Furthermore, this permits control over the trajectory of the pedicle screw so that it may be more accurately secured to the vertebral body (i.e. the pedicle screw must be rigid such that the shank of the pedicle screw is fixed in relation to the insertion instrument). Therefore, many polyaxial pedicle screw drivers are designed to engage the pedicle screw such that the tulip and shank of the screw are rigidly coupled, thereby permitting the pedicle screw to be driven into the vertebra with greater control.
One example of an instrument is disclosed in U.S. Pat. No. 8,231,635. The disclosed insertion instrument includes a polyaxial screwdriver wherein the polyaxial screwdriver both threads into the tulip of the pedicle screw and engages the head of the pedicle screw to maintain the tulip and screw in a rigid configuration relative to each other. The polyaxial screwdriver further includes a locking mechanism to couple the polyaxial screwdriver to the pedicle screw such that the pedicle screw cannot rotate with respect to the polyaxial screwdriver. The locking mechanism further prevents the polyaxial screwdriver accidentally unthreading from the tulip of the pedicle screw (i.e. a one way ratcheting system is employed). In order to remove the polyaxial screwdriver from the pedicle screw, a button must be pressed and held which releases the ratchet and permits the polyaxial screwdriver to be unthreaded from the tulip without backing out the pedicle screw from the vertebral body.
It would be preferable, however, if the clinician can selectively lock or unlock the driving member of the screw insertion instrument such that the instrument remains in the position in which the clinician left it (i.e. the clinician does not need to continuously provide input to keep the pedicle screwdriver disengaged from the screw head).
There remains a need for an instrument for inserting spinal anchors.